[llvm] [RISCV][ISel] Add codegen support for the experimental zabha extension (PR #80192)

[Yingwei Zheng via llvm-commits]

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@@ -19519,8 +19522,14 @@ RISCVTargetLowering::shouldExpandAtomicRMWInIR(AtomicRMWInst *AI) const {
     return AtomicExpansionKind::None;
 
   unsigned Size = AI->getType()->getPrimitiveSizeInBits();
-  if (Size == 8 || Size == 16)
-    return AtomicExpansionKind::MaskedIntrinsic;
+  if (Size == 8 || Size == 16) {
+    if (!Subtarget.hasStdExtZabha())
+      return AtomicExpansionKind::MaskedIntrinsic;
+    else if (AI->getOperation() == AtomicRMWInst::Nand)
+      return Subtarget.hasStdExtZacas() ? AtomicExpansionKind::CmpXChg
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dtcxzyw wrote:

Related patch: https://github.com/llvm/llvm-project/pull/80119

https://github.com/llvm/llvm-project/pull/80192